The present invention relates to a combination valve, particularly for a secondary air blower in internal combustion engines with a controlled three-way catalyst.
Such combination valves or combo-valves contain a shut-off valve and a check valve in a valve housing and serve for switching the secondary air stream for the exhaust gas line of internal combustion engines with controlled three-way catalysts. With such a blower, or so-called secondary air blower, fresh air is supplied before the catalyst to the exhaust gas line of the internal combustion engine for providing a post-combustion of the exhaust gas at temperatures of over 600.degree. C. in the line. The post-combustion reduces hydrocarbon compounds and the carbon monoxide contained in the exhaust gas. Moreover, the post-combustion supplies heat to the catalyst, which is very important for the cold start.
During the operation of the secondary air blower the shut-off valve is opened and the secondary air is blown after passing through open check valve into the exhaust gas line of the internal combustion engine. The check valve has the function to prevent a return stream of the exhaust gas through the blower during a pressure increase in the exhaust gas line. The shut-off valve prevents a suction of secondary air caused by pressure pulsations during stoppage of the secondary air blower.
In a combi-valve of the above mentioned type it has been proposed to load the valve member of the shut-off valve in a valve opening direction with a differential pressure between a valve inlet pressure and a surrounding pressure and to provide a flat spring associated with the valve plate with a plurality of valve openings which are covered by the flat spring in its closing position. This is disclosed for example in the German document DE 42 04 425.4. The flat spring has a plurality of spirals which are punched in it and is centrally clamped between the valve plate and the stroke guard. For this purpose the flat spring has only a low restoring force so that only low pressure losses during a throughflow through the combi-valve occur. Due to the low mass inertia of the flat spring a fast reaction of the check valve is guaranteed.
During the operation of such a combination valve in a secondary air circuit of an internal combustion engine has been shown that the check valve in certain operational conditions of the internal combustion engine, for example during fast load engage, can be untight. As a result, after switching off of the secondary blower the shut-off valve no longer closes since pressure acting on the valve member of the shut-off valve through the untight check valve remains open at the valve outlet of the valve member of the shut-off valve.